The present invention relates to an imaging method and apparatus for displaying computer-modeled objects present in the form of a grid model, in which the objects are defined by the coordinates of the node points of the grid model and the optical properties of the polygon surfaces between the node points, and the individual polygon surfaces are divided into a plurality of scanlines and pixels. The image impression is calculated in only a portion of the pixels according to a local illumination model, or a portion of a local illumination model, and is interpolated in the remaining pixels from the previously-calculated image-information values for reducing the calculation effort.
In computer-graphics systems, objects are usually simulated with grid models, in which the objects are defined by the spatial coordinates of the node points of the grid model and the optical properties, such as the color and reflection behavior, of the polygon surfaces between the node points. Computer-graphics systems of this type are known from, for example, VOORHIES, D.; FORAN, J.: Reflection Vector Shading Hardware, SIGGRAPH '94, and JACKEL, D.; Russeler, H.:A Real Time Rendering System with Normal Vector Shading; 9th Eurographics Workshop on Graphics Hardware, Oslo (Norway), 1994. To calculate the image impression, the individual polygon surfaces are divided into pixels, and the spatial coordinates and the spatial position of the local surface normal, which are decisive for the reflection behavior and thus the impression of the image, are calculated for each pixel. With an inclination of the local surface normal inside the polygon surface, for example, it is also possible, on the one hand, to simulate curved polygon surfaces, so a smooth and thus visually inconspicuous transition can be attained at the edges between adjacent polygon surfaces. On the other hand, it is also possible to simulate rough textures in this manner by inclining the local surface normal inside the respective polygon surface to correspond to the desired texture, which is also referred to as bump-mapping. After the spatial coordinates of the individual pixels and the respective local surface normal have been calculated, the image impression is calculated individually for each pixel, according to a local illumination model; the perspective of the viewer, the spatial position and the optical properties of the pixel, the orientation of the local surface normal and the spatial position and optical properties of the light sources that illuminate the objects are all considered.
Typically, the illumination model used to calculate the image impression of the individual pixels is the one described in PHONG: Illumination for Computer Generated Pictures; Communications of the ACM, 18(6):311-317, June 1975, which has also been incorporated into the quasi-industry standard OpenGL. This illumination model advantageously permits the consideration of numerous optical effects, such as ambient, diffuse and specular reflection, and thus produces a very realistic image impression.
A disadvantage of the known imaging methods based on a local illumination model is the relatively large amount of calculation effort. In a software-based solution, the serial processing of the calculation steps increases the time span necessary for calculating an image, which hinders a real-time display of representations of movement, particularly with complex illumination relationships. In a hardware-based solution, the increased calculation effort can be overcome with a plurality of pipelines operating in parallel, but this arrangement is associated with a larger chip surface.